Conventional approaches to vaccine development have implemented either whole replication competent virus which has been attenuated (e.g. Sabin polio vaccine, measles, mumps, rubella (MMR)) or inactivated virions that are not replication competent. On occasions, the inactivated virus vaccines may include split vaccines where the virus particles have been disrupted. Molecular techniques have also been used to develop the subunit vaccine (e.g. hepatitis B vaccine) that consists only of the surface glycoproteins of hepatitis B virus. The inactivated virus vaccines tend to induce primarily antibody responses to the viruses in question, whereas the live attenuated vaccines induce both cell-mediated immunity as well as an antibody response since the vaccine induces a transient infection.
The only disease which has been eliminated by virtue of a successful vaccination campaign is smallpox. A campaign is currently in progress to eradicate polio. Features of virus infections that can be eliminated by vaccination are infections caused by viruses with stable virus antigens (i.e. very low mutation frequency, few subtypes), that lack a reservoir in other animal species, viruses that do not persist in the body once the infection is over and where vaccination leads to long lasting immunity. Viruses such as polio and measles fulfill these criteria whereas viruses such as influenza virus (Flu), HCV, and HIV that vary their protein sequences do not. It is for this reason that new and alternate approaches are required to develop vaccines for these diseases.
Vaccination aims to stimulate the immune response to a specific pathogen in advance of infection. When an individual is exposed to that pathogen, a memory response is triggered which prevents the establishment of infection. Vaccines therefore stimulate the adaptive immune response which unlike innate immunity, is long lived and has memory. There are two major arms to the adaptive immune system. Humoral immunity which involves the development of antibodies that can bind virus particles and certain antibodies that can neutralize infection. Cell mediated immunity that leads to the development of cytotoxic T-cells that kill infected cells exposing viral epitopes in the context of human leukocyte antigen (HLA) class I, in this way eliminating infected cells.
The challenge of providing vaccines suitable for stimulation of the adaptive immune system is that peptide epitopes need to be taken up by the antigen presenting cells.
Several peptides have been demonstrated to translocate across the plasma membrane of eukaryotic cells by a seemingly energy-independent pathway. These peptides are defined as cell-penetrating peptides (CPPs). Cellular delivery using these cell-penetrating peptides offers several advantages over conventional techniques. It is non-invasive, energy-independent, is efficient for a broad range of cell types and can be applied to cells en masse.
For humoral responses and development of antibodies it may not be needed to obtain cell-penetrating properties since stimulation of B-cells are also done by extracellular peptide antigens. Hepatitis means inflammation of the liver which can be caused by a variety of factors including toxins, certain drugs, some diseases, heavy alcohol use, and bacterial and viral infections. Hepatitis is also the name of a family of viral infections that affect the liver; the most common types in the developed world are hepatitis A, hepatitis B, and hepatitis C.
Hepatitis C is a liver disease that results from infection with the hepatitis C virus (HCV). It can range in severity from a mild illness lasting a few weeks to a serious, lifelong illness. Hepatitis C is spread via blood; the most common form of transmission is through sharing needles or other equipment used to inject drugs. The infection can be either “acute” or “chronic”. Acute HCV infection is an asymptomatic, short-term illness that occurs within the first 6 months after someone is exposed to the hepatitis C virus. For most people, acute infection leads to chronic infection, which can result in long-term complications and even death.
HCV is an enveloped positive stranded ribonucleic acid (RNA) virus with a diameter of about 50 nm, belonging to the genus Hepacivirus in the family Flaviviridae that replicate in the cytoplasm of infected cells. The only known reservoir for HCV is humans, although the virus has experimentally been transmitted to chimpanzees. The natural targets of HCV are hepatocytes and possibly B-lymphocytes. As of 2008, six different genotypes and more than 100 subtypes of the virus are known. Replication occurs through an RNA-dependent RNA polymerase that lacks a proofreading function, which results in a very high rate of mutations. Rapid mutations in a hypervariable region of the HCV genome coding for the envelope proteins enable the virus to escape immune surveillance by the host. As a consequence, most HCV-infected people proceed to chronic infection.
It is estimated that 170 million people are infected with HCV worldwide, equating to approximately 3% of the global population. There are also approximately 3-4 million people who are infected every year; with an estimated 80% of these newly infected patients progressing to chronic infection.
The 6 genotypes of HCV have different geographical spread. The disease in the early stages is generally asymptomatic; the majority of patients with chronic infection eventually progress to complications such as liver fibrosis and cirrhosis, and, in 1-5% of cases, hepatocellular carcinoma.
HCV is the major cause of non-A, non-B hepatitis worldwide. Acute infection with HCV frequently leads to chronic hepatitis and end-stage cirrhosis. It is estimated that up to 20% of HCV chronic carriers may develop cirrhosis over a time period of about 20 years and that of those with cirrhosis between 1 to 4% is at risk to develop liver carcinoma.
The about 9.6 kb single-stranded RNA genome of the HCV virus comprises a 5′- and 3′-noncoding region (NCRs) and, in between these NCRs a single long open reading frame of about 9 kb encoding an HCV polyprotein of about 3000 amino acids.
HCV polypeptides are produced by translation from the open reading frame and cotranslational proteolytic processing. Structural proteins are derived from the amino-terminal one-fourth of the coding region and include the capsid or Core protein (about 21 kDa), the E1 envelope glycoprotein (about 35 kDa) and the E2 envelope glycoprotein (about 70 kDa, previously called NS1), and p7 (about 7 kDa). The E2 protein can occur with or without a C-terminal fusion of the p7 protein (Shimotohno et al. 1995). An alternative open reading frame in the Core-region has been found which is encoding and expressing a protein of about 17 kDa called F (Frameshift) protein (Xu et al. 2001; Ou & Xu in US Patent Application Publication No. US2002/0076415). In the same region, ORFs for other 14-17 kDa ARFPs (Alternative Reading Frame Proteins), A1 to A4, were discovered and antibodies to at least A1, A2 and A3 were detected in sera of chronically infected patients (Walewski et al. 2001). From the remainder of the HCV coding region, the non-structural HCV proteins are derived which include NS2 (about 23 kDa), NS3 (about 70 kDa), NS4A (about 8 kDa), NS4B (about 27 kDa), NS5A (about 58 kDa) and NS5B (about 68 kDa) (Grakoui et al. 1993).
Influenza remains a significant cause of mortality and morbidity worldwide. The World Health Organisation (WHO) estimates that seasonal epidemics affect 3-5 million people with severe illness annually and result in 250,000-500,000 mortalities. Influenza is caused by viruses in the family Orthomyxoviridae which are negative stranded RNA viruses. The influenza virus exists as three types, A, B and C of which only A is associated with pandemics. Types A viruses are found in both humans and animals, particularly birds but also other mammals such as pigs. Type A viruses are further typed into subtypes according to different kinds and combinations of virus surface proteins. Among many subtypes in 2009 influenza A (H1N1) and A (H3N2) subtypes were circulating among humans. Influenza A and B are included in the seasonal vaccine, whereas influenza C occurs only rarely, and so it is not included in the seasonal vaccine. Type B viruses are human specific and Type C viruses cause a very mild disease. The genomes of Orthomyxoviruses are segmented. Influenza viruses Types A and B have 8 segments whereas type C has seven. Pandemics may arise as a result of re-assortment of gene segments when two different type A viruses infect the same cell. There is no immunity in the population to this novel re-assorted virus. Three pandemics occurred in the twentieth century: “Spanish influenza” in 1918, “Asian influenza” in 1957, and “Hong Kong influenza” in 1968. The 1918 pandemic killed an estimated 40-50 million people worldwide. Subsequent pandemics were much milder, with an estimated 2 million deaths in 1957 and 1 million deaths in 1968. In June 2009 the WHO declared a pandemic from influenza virus H1N1 (swine Influenza) which was declared over in August 2010.
Human papillomaviruses are made up of a group of DNA viruses in the family Papillomaviridae which infect the skin and mucous membranes. Two groups which are derived from more than 100 different identified subtypes are the main cause for clinical concern: those causing warts (both benign and genital warts), and a group of 12 “high risk” subtypes that can result in cervical cancer. This latter group has been attributed as a contributory factor in the development of nearly all types of cervical cancer. Worldwide, cervical cancer remains the second most common malignancy in women, and is a leading cause of cancer-related death for females in developing countries. HPV 16 and 18 have been mainly associated with cervical cancer, however, the virus is also a cause of throat cancer in both men and women. HPV is transmitted through contact and enters the skin through abrasions. An abortive infection, where only the early proteins are expressed is associated with cancer development.